1. Field of the Invention
This invention relates to the efficient operation of engine exhaust treatment systems, and more particularly relates to the delivery of a dosant to exhaust treatment systems.
2. Description of the Related Art
Stricter environmental regulations in the United States and Europe are requiring the use of exhaust treatment devices such as particulate filters and/or catalytic devices on engines to reduce harmful emissions including nitrogen oxides (NOx), hydrocarbons, carbon monoxide, and particulate matter. Leading exhaust treatment devices, such as particulate filters, NOx adsorbers, and Selective Catalytic Reduction (SCR) sub-systems, benefit from—and even rely upon—the thermal and chemical conditioning of exhaust being feed to these treatment devices.
For example, NOx adsorbers require the injection of a chemical dosant for regeneration. A dosant, such as aqueous urea or various hydrocarbon fuels, serves as a reductant. This injected reductant creates a saturated reductant-to-oxygen ratio in the conditioned exhaust. Excess reductant drives the nitrates from the NOx adsorber site and converts the nitrates to nitrogen, thereby regenerating the NOx adsorber.
However, dosant delivery systems require additional components and additional space. Space is usually at a premium around engines and their related components, particularly on trucks or other moving vehicles, and it is desirable that the additional exhaust treatment components be compacted into as small a space as possible. The problem of efficient use of exhaust stream dosants makes the issue of space more difficult, since many dosants, after being injected or “dosed” into the exhaust stream, need to mix, undergo chemical change, be evaporated, or otherwise be modified from their original injected form before encountering exhaust treatment components such as flow-through catalytic devices or particulate filters.
Hydraulic and thermal energy present in engine exhaust can be used to atomize, disperse, vaporize, mix, and/or transport a dosant. The use of an engine byproduct, such as engine exhaust, to disperse a dosant can reduce the number of additional components and additional space required to implement a dosant delivery system. However, the channeling of engine exhaust can itself present additional problems that can also require additional components and additional space to address.
Several approaches exist to regulate and control the flow of engine exhaust through dosant deliver systems. Such approaches generally address problems like changing exhaust supplies and temperatures and unwanted exhaust pressure buildup in the dosant delivery system. To address these problems, previous approaches have relied upon additional components, which occupy additional space.
One approach relies on such additional components as a carbon chamber, a feedback into the intake manifold, a pressure relief valve, a solenoid coil, and a vacuum responsive modulator. These additional components and the space they occupy mitigate the advantages of using engine exhaust to disperse a dosant.
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method that can control a fraction of engine exhaust used to deliver a dosant without an excess of additional space and component requirements.